Platelets as a source of growth-promoting factor(s) for tumor cells.

Human platelet lysate was shown to contain growth-promoting activity for four well-established malignant cell lines. Platelet lysate was able to support their cell proliferation without plasma or serum, indicating that platelets contained "survival factor" as well as mitogenic factor for these tumor cells. The growth-promoting activity was nondialyzable, heat stable up to 56 degrees, and partially trypsin labile, but it was completely destroyed by periodate oxidation, suggesting that a glycoprotein or glycopeptide may be the active principle. The activity was released from platelets aggregated by thrombin or collagen but not by adenosine diphosphate. This suggests that alpha-granules may be the principle storage site for growth-promoting activity.